High power yig filter

ABSTRACT

A high power YIG filter is disclosed which employs a YIG sample and a dielectric resonator for coupling energy from a first transmission line to a second transmission line. An adjustable magnetic field is applied to the YIG sample to tune the frequency of the high power YIG filter. A low pass filter is connected to the output of the high power YIG filter to suppress various modes in the combined YIG sample and dielectric resonator. A circulator connects the low pass filter to the output of the high power YIG filter.

United States Patent Weiner Oct. 14, 1975 [54] HIGH POWER YIG FILTER 3,517,351 6/1970 Grossbach 333/73 W 3,629,735 12/1971 Carter et a1... 333/17 [75] Inventor: ri wemer Ocean Tmvnshlp, 3,740,675 6/1973 Moore et a1. 333 73 R [73] Assignee: The United States of America as Primary 'f Lawrence represented b th Secretary of th Assistant Examiner Marvin Nussbaum A W hi DC Attorney, Agent, or FirmNathan Edelberg; Robert P.

Gibson; Arthur Boatright [22] Filed: Aug. 21, 1974 Appl. No.: 499,256

U.S. Cl 333/73 R; 333/73 S; 333/73 W Int. Cl. HOIP l/20; l-lOlP 3/08; 1101? 7/00 [58] Field of Search... 333/73 R, 73 S, 73 W, 83 R, 333/82 R, 82 B, 82 BT, 24.2, 24.1, 17 R, 17 L, 1.1

[56] References Cited UNITED STATES PATENTS 3,274,519 9/1966 Nathanson 333/73 W 3,500,256 3/1970 Carter et a1 333/17 [57] ABSTRACT 9 Claims, 2 Drawing Figures IIIIIIIIIIIIIIIII III 111/1111 U.S. Patent Oct. 14, 1975 N wN HIGH POWER YIG FILTER The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

FIELD OF THE INVENTION This invention relates to microwave filters and particularly to high power microwave filters.

BACKGROUND OF THE INVENTION Tunable band pass microwave filters have been constructed from two transmission lines interconnected by a YIG sample. Such filters have been tuned by applying an adjustable magnetic bias field to the YIG sample. The YIG sample passes energy from the first transmission line to the second transmission line at its resonant frequency. The resonant frequency of the YIG sample is altered by the magnetic bias field and therefore the filter can be tuned.

The above filters suffer from a major drawback in that the YIG sample ceases to couple energy from the first transmission line to the second transmission line when the power level of the signal being coupled exceeds a threshold value. Typically, the above filters are not operable above 100 milliwatts at frequencies in the range of 12 GHz.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the teaching of this invention it has been found that when the YIG sample is mounted adjacent to a dielectric resonator, the composite thereof will couple energy at high power levels over a range of frequencies. As a result of this, a high power YIG filter has been developed which includes an input transmission line, an output transmission line, and a YIG sample associated with a dielectric resonator for connecting the input transmission line to the output transmission line, where the dielectric resonator has a frequency of f,,. A low pass filter having a cutoff frequency of f,, is connected to the output of the output transmission line and an adjustable magnetic field is applied to the YIG sample.

In the preferred embodiment, a circulator, having its isolated port terminated in its characteristic impedance connects the output of the output transmission line to the low pass filter.

DESCRIPTION OF THE DRAWING For a more complete understanding of this invention, reference should be made to the following detailed description of the invention and drawings in which:

FIG. 1 is a section view taken along the line l-l of FIG. 2, showing the placing of a YIG sample and dielectric disk in a high power YIG filter embodying the principles of this invention; and

FIG. 2 is a diagram partially in block diagram form and partially a section view taken along the line 2-2 of FIG. 1, showing a high power YIG filter embodying the principles of this invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the Figures, we see an input strip transmission line and an output strip transmission line 11. The input strip transmission line 10 and output transmission strip line 11 have shorting end walls 8 and 9 respectively and share a common wall 12 which has mounted in a slot therein a YIG sample 13 adjacent to a dielectric resonator 14. The transmission lines 10 and 11 could also be coaxial lines or waveguides.

As is well known, the YIG sample 13 has a relatively linear resonant frequency as a function of magnetic field bias over a range of magnetic field biases, if the energy incident thereupon is below a prescribed power level. The dielectric resonator 14, on the other hand, has a resonant frequency f which is independent of magnetic field bias. When the YIG sample 13 is mounted adjacent to the dielectric resonator 14, the composite device which results therefrom has several resonant frequencies (in different modes) as a function of magnetic field bias. Therefore, it can be seen that each of the devices 13 and 14 have single valued functions of resonant frequencies versus magnetic field bias, while the composite device exhibits a multi-valued function of resonant frequency versus magnetic field bias. For a more complete discussion of the above see my article entitled Electromagnetic Effects in Magnetic Insulators which appeared in the Journal of Applied Physics, Volume 43, number 3 in the March 1972 issue. This article is incorporated herein by reference.

The composite device resulting from the association of the YIG sample 13 and the disk resonator 14 will be sensitive to power level below a prescribed frequency 12,. Above the prescribed frequency 1",. the combined device, unlike the YIG sample 13 by itself, will be relatively insensitive to power level. Therefore, the composite device can operate at a much higher power level than the previously known YIG filters. The problem with employing the composite device is the multivalued function resulting therefrom of resonant frequency versus magnetic field bias. Basically, there are several modes in which the combined device will operate. There are two basic responses, one below the resonant frequency fl, of the dielectric resonator 14 and the other, above the frequency f,,. Further, there are spurious modes which result from excitation of the combined device. These spurious modes also fall above the resonant frequency fi of the dielectric resonator 14.

Therefore, the output of the output transmission line 11 is connected via a circulator 16 to a low pass filter 17 which passes all frequencies below the resonant frequency f of the dielectric resonator 14. In this way, the transfer function of the overall device from the input device 15 to the output of the low pass filter 17, will be a single valued function.

The circulator 16 has an isolated port 18 which is terminated in characteristic impedance termination 19 to absorb the energy rejected by the low pass filter 17 which results from the unwanted modes of the composite device resulting from the association of the YIG sample 13 and the dielectric resonator 14.

A coil 21 provides a variable magnetic field to the sample 14 for tuning the device shown in the figure. Current from a voltage source is applied via leads 22 and 23, resistor 24 and potentiometer 26 to provide the adjustable magnetic field. The value of the resistor 24 and the voltage source limit the maximum magnetic field applicable, while the maximum value of the resistance of the variable resistor 26 is varied in order to obtain the frequency at which filtering is desired.

Therefore, it can be seen by using a composite device, including a YIG sample 13 and a dielectric resonator 14, to interconnect to transmission lines, rather than a YIG sample by itself and connecting the low pass filter 17 to the output of the transmission line 11 via the circulator 16, a band pass filter is provided operating at higher power levels than YIG filters have been operatable at heretofore.

While this invention has been described with respect to a particular embodiment thereof, numerous others will become obvious to those of ordinary skill in the art in light thereof.

What is claimed is:

l. A high power YIG filter including an input transmission line;

anoutput transmission line;

a YIG sample mounted in close proximity and coupled to a dielectric resonator for connecting said input transmission line to said outputtransmission line, said dielectric resonator having a resonant freq y fit;

a low pass filter having a cutoff frequency of f means for connecting said output transmission line to said low pass filter; and

means for applying an adjustable magnetic field to said YIG sample.

2. The high power YIG filter as defined in claim 1 in which said connecting means includes a circulator having an input port, an output port and an isolated port; said output transmission line being connected to said input port and a termination connected to said isolated port.

field is adjustable between a first value and a second value.

4. The high power YIG filter as defined in claim 3 in V which said connecting means includes a circulator having an input port, an output port and an isolated port; said output transmission line being connected to said i'nput portand a termination connected to said isolated port.

made from a strip line.

6. The high power YIG filter as defined in claim 5 in which said input transmission line has an input end and an output end, and said output end is shorted.

7. The high power YIG filter as defined in claim6 in which said output transmission line has an input end.

9. The high power YIG filter as defined in claim 8 in which said YlG sampleand said dielectricresonator are mounted adjacent to said shared outer conductor. l

3. The high power YIG filter as defined in claim 1 in which said means for applying said adjustable magnetic 5. The high power YIG filter as definedin claim 4 in I which said input and output transmission lines are 

1. A high power YIG filter including an input transmission line; an output transmission line; a YIG sample mounted in close proximity and coupled to a dielectric resonator for connecting said input transmission line to said output transmission line, said dielectric resonator having a resonant frequency fd; a low pass filter having a cutoff frequency of fd; means for connecting said output transmission line to said low pass filter; and means for applying an adjustable magnetic field to said YIG sample.
 2. The high power YIG filter as defined in claim 1 in which said connecting means includes a circulator having an input port, an output port and an isolated port; said output transmission line being connected to said input port and a termination connected to said isolated port.
 3. The high power YIG filter as defined in claim 1 in which said means for applying said adjustable magnetic field is adjustable between a first value and a second value.
 4. The high power YIG filter as defined in claim 3 in which said connecting means includes a circulator having an input port, an output port and an isolated port; said output transmission line being connected to said input port and a termination connected to said isolated port.
 5. The high power YIG filter as defined in claim 4 in which said input and output transmission lines are made from a strip line.
 6. The high power YIG filter as defined in claim 5 in which said input transmission line has an input end and an output end, and said output end is shorted.
 7. The high power YIG filter as defined in claim 6 in which said output transmission line has an input end and an output end, and said input end of said output transmission line is shorted.
 8. The high power YIG filter as defined in claim 7 in which said input and output transmission lines share a common outer conductor.
 9. The high power YIG filter as defined in claim 8 in which said YIG sample and said dielectric resonator are mounted adjacent to said shared outer conductor. 